Our overall aims are to elucidate the biochemical mechanisms underlying the biological role of mineralocorticoids, particularly aldosterone, in lactation, e.g. sodium conservation by the mammary gland. Our specific aims are: (a) Isolation and identification of the major metabolites of (3H)aldosterone, including acylated metabolites obtained in the less polar fractions in incubation experiments with mammary tissues from lactating rats. (b) Elucidation of the molecular mechanisms underlying the biological role of aldosterone in lactation, e.g., determination of the association constants for the binding of the acylated metabolites of (3H)aldosterone to the receptors for adrenocorticoids in the cytosol and nuclear fractions of mammary tissues from lactating rats.